Egr cooler

ABSTRACT

An EGR cooler includes: a casing in which cooling water flows; a plurality of tubes in which exhaust gas flows, the plurality of tubes being housed in the casing; a header plate to which ends of the plurality of tubes are bonded, the header plate being bonded to an end of the casing; an inlet tank into which the exhaust gas is introduced, the inlet tank being bonded to the end of the casing; and a shielding member being provided in the inlet tank to shield a circumferential wall of the inlet tank from the introduced exhaust gas.

TECHNICAL FIELD

The present invention relates to an EGR (Exhaust Gas Recirculation) cooler.

BACKGROUND ART

Some typical EGR systems usable in a diesel engine are provided with an EGR cooler for cooling exhaust gas to be returned to an air-intake side. The EGR cooler includes a plurality of tubes through which exhaust gas passes and a casing (sometimes called as a “shell”) in which these tubes are housed. The casing has a first end that defines an inlet through which cooling water is introduced and a second end that defines an outlet through which the cooling water is discharged.

The casing is formed in a cylindrical shape. An opening of the first end of the casing is provided with an inlet tank into which exhaust gas is introduced and from which the exhaust gas is discharged into the tubes. An end of the second end of the casing is provided with an outlet tank from which the exhaust gas from the tubes is discharged. Both ends of each tube in the casing are fixed to header plates by brazing or the like. The header plates are fixed to the inner circumferential surface of the casing by welding to close the openings of the casing. In other words, in the casing, both ends of which are closed by the header plates, cooling water flows outside the plurality of tubes while the exhaust gas flows inside the tubes.

In the inlet tank, since one surface of the header plate, i.e., the surface opposed to the inlet tank, is directly exposed to the exhaust gas having a high temperature, a brazed portion between the header plate and each tube is heated to a high temperature by the exhaust gas, which lowers the bonding strength therebetween and thus causes a crack in the brazed portion.

In view of the above, in order to prevent the header plate from being directly exposed to the exhaust gas, there has been suggested an arrangement of an EGR cooler in which a shielding plate in substantially the same shape as that of the header plate is provided at the upstream side of the header plate and the tube end is extended to the shielding plate (e.g., Patent Literature 1).

According to this arrangement, since a double-layered structure is provided between the inlet tank and the inner side of the casing, the header plate is not exposed to the exhaust gas having a high temperature introduced into the inlet tank and thus the temperature of the brazed portion to each tube is restrained from becoming high. Thus, the brazed portion is unlikely to have any crack and leakage of the cooling water from the casing can be prevented.

CITATION LIST

Patent Literature

Patent Literature 1: JP-A-2000-45882

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In the EGR cooler as disclosed in the above patent literature, although the brazed portion can be prevented from being directly exposed to the exhaust gas, a circumferential wall (bonnet) in the inlet tank is still directly exposed to the exhaust gas. Thus, the inlet tank suffers from a large outward thermal expansion of the circumferential wall, which results in a difference in thermal expansion between the inlet tank and the casing and the header plate to which the inlet tank is fixed. In other words, while the temperatures of the casing and the header plate are not so increased with a resulting small degree of thermal expansion because the majority thereof is exposed to the cooling water, the circumferential wall of the inlet tank suffers from a considerable thermal expansion because the circumferential wall is exposed only to the exhaust gas without being exposed to the cooling water.

Thus, at the bonding portion between the inlet tank and the casing and the header plate, the considerable thermal expansion of the inlet tank causes the outward deformation of the casing and the header plate. As a result of this deformation, a high stress is generated to cause a crack in the bonding portion between the header plate and each tube.

An object of the invention is to provide an EGR cooler capable of restraining thermal deformation resulting from a large difference in thermal expansion as compared with an inlet tank to prevent occurrence of a crack.

Means for Solving the Problems

According to an aspect of the invention, an EGR cooler includes: a casing in which cooling water flows; a plurality of tubes in which exhaust gas flows, the plurality of tubes being housed in the casing; a header plate to which ends of the plurality of tubes are bonded, the header plate being bonded to an end of the casing; an inlet tank into which the exhaust gas is introduced, the inlet tank being bonded to the end of the casing; and a shielding member being provided in the inlet tank to shield a circumferential wall of the inlet tank from the introduced exhaust gas.

In the EGR cooler, it is preferable that the shielding member is provided in the inlet tank.

In the EGR cooler, it is preferable that a clearance is formed between the shielding member and the header plate.

In the EGR cooler, it is preferable that an opening of an exhaust gas outlet of the shielding member covers entrances of all the tubes.

In the EGR cooler, it is preferable that the shielding member is gradually widened toward an exhaust gas outlet.

In the EGR cooler, it is preferable that the opening of the exhaust gas outlet is provided with a cylindrical outlet end having a diameter substantially constant along a flow direction of the exhaust gas.

According to the aspect of the invention, the shielding member is provided in the inlet tank. Since the exhaust gas having a high temperature introduced into the inlet tank is unlikely to contact with the circumferential wall of the inlet tank, the outward thermal expansion of the circumferential wall is restrained. Thus, the casing and the header plate bonded to the inlet tank are not affected by the thermal expansion of the inlet tank, so that a large deformation in the casing and header plate is unlikely to occur. As a result, generation of a large stress is prevented at the bonding portion between the header plate and each tube and thus no crack occurs.

According to the arrangement in which the shielding member is provided in the inlet tank, since a core, i.e., the header plate and the tubes, is not provided with the shielding member, the front and rear configurations of the core are identical. Thus, the core is not inadvertently installed back to front in a casing whose front and rear sides are not invertible, which facilitates an assembling process.

With the clearance formed between the shielding member and the header plate, even when the shielding member is exposed to the exhaust gas and thus thermally expanded, the shielding member is prevented from contacting with the header plate. Thus, the header plate is prevented from being pressed to generate stress.

According to the arrangement in which the opening of the outlet of the shielding member is sufficiently large to cover the ends of all the tubes, the exhaust gas from the shielding member can be equally fed into the tubes, thereby cooling the exhaust gas with an improved efficiency.

With the shielding member gradually widened toward the outlet, even when the inlet casing has a small opening area at the inlet thereof while having a large opening area at the outlet thereof, the exhaust gas can be reliably guided into the tubes, thereby providing a favorable cooling efficiency.

According to the arrangement in which the outlet end for restraining diffusion is provided to the outlet of the shielding member, the exhaust gas can be fed into the tubes without diffusion. Thus, a flow of the exhaust gas becomes smooth, so that cooling efficiency can be further improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of an EGR cooler according to an exemplary embodiment of the invention along a flow direction of exhaust gas.

FIG. 2 is a sectional view taken along the line II-II in FIG. 1.

FIG. 3 is an enlarged view showing a primary part of the EGR cooler.

FIG. 4 is a view showing components used in the EGR cooler.

FIG. 5 is a sectional perspective view showing the components.

FIG. 6 is a sectional view showing a modification of the invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

An exemplary embodiment of the invention will be described below with reference to the attached drawings.

FIG. 1 is a sectional view of an EGR cooler 10 according to this exemplary embodiment along a flow direction of exhaust gas (see a hatched arrow). FIG. 2 is a sectional view taken along the line II-II in FIG. 1. FIG. 3 is an enlarged view showing a primary part of the EGR cooler 10. FIG. 4 is a view showing components used in the EGR cooler 10 and FIG. 5 is a sectional perspective view thereof In the following description, “front” means the upstream side of a flow of exhaust gas and “rear” means the downstream side. Further, “right and left” means right and left when viewed from the front.

Referring to FIG. 1, the EGR cooler 10 includes: a cylindrical casing 11; a plurality of flattened tubes 12 for exhaust gas circulation housed in the casing 11; opposed header plates 13 to which the ends of the tubes are bonded; and an inlet tank 14 and an outlet tank 15 bonded to the casing 11 via the header plates 13, respectively. The inlet tank 14 is provided with an attachment flange 16 having an inflow opening 16A. The outlet tank 15 is provided with an attachment flange 17 having an outflow opening 17A.

Cylindrical projections 18 are formed at first and second ends of the casing 11, the projections 18 each having a diameter slightly larger than the diameter of a center body of the casing 11. Provided on the lower side of front one of the projections 18 is an inflow opening 21 through which cooling water (see an outlined arrow) is introduced into the casing 11. Provided on the upper side of rear one of the projections 18 is an outflow opening 22 through which cooling water is discharged from the casing 11. Provided on the top of the projection 18 having the inflow opening 21 for cooling water are a pair of degassing holes 23 circumferentially arranged at a distance corresponding to a predetermined angle (only one of them being shown in FIG. 1).

Referring to FIG. 2, gaps between opposed surfaces of the tubes 12 arranged side by side serve as cooling water passages 24 through which cooling water passes. All the cooling water passages 24 are preferably designed to have the same width. According to this exemplary embodiment in which the tubes 12 are arranged side by side in a right-and-left direction, the inflow opening 21 for cooling water (FIG. 1) is located on the lower side of the projection 18 so that cooling water from the inflow opening 21 immediately enters the cooling water passages 24. In view of the above, the inflow opening 21 is preferably located at the lower central portion of the projection 18 as in this exemplary embodiment. In other words, according to this exemplary embodiment, immediately after cooling water is introduced through the inflow opening 21, a flow direction of the cooling water coincides with the vertical direction of the tubes 12, so that a flow of the cooling water is not hampered.

Further, according to this exemplary embodiment, the surfaces of the tubes 12 are partly brazed to one another at dot-like projections while the header plates 13 are brazed to the ends of the tubes 12 (the detailed illustration thereof is omitted). A combination including the tubes 12 and the header plates 13 serves as a core 25.

For assembling the EGR cooler 10, the core 25 is produced in advance by brazing the tubes 12 to one another and then brazing the header plates 13 to the tubes 12. The core 25 is housed in the casing 11 provided by upper-and-lower or right-and-left halved structures, namely casing halves 11A and 11B. The casing halves 11A and 11B are bonded to each other by welding or the like. The tanks 14 and 15 are attached to the ends of the casing 11 (header plates 13) by welding or the like, respectively.

For the attachment, as shown in FIG. 3 in an enlarged manner, cylindrical portions 131 formed on the outer circumferences of the header plates 13 are fitted in opening ends 111 of the casing 11, respectively, while opening ends 141 and 151 of the tanks 14 and 15 are fitted in the cylindrical portions 131, respectively, and all of them are bonded together by welding. Incidentally, according to this exemplary embodiment, the contour of each of the opening ends 111, 141 and 151 and the cylindrical portions 131 is not a circle but a slightly square-like deformed shape, which is exemplified by the contour of the opening end 141 of the inlet tank 14 in FIG. 4.

A detailed description will be made below on the inlet tank 14 used in this exemplary embodiment with reference to FIGS. 1, 4 and 5. The inlet tank 14 includes: a cylindrical inlet end 142 fitted in the inflow opening 16A of the attachment flange 16; the opening end 141 that defines the outlet; and a circumferential wall 143 that connects the ends 141 and 142 to each other. The circumferential wall 143 is gradually widened from the inlet end 142 toward the opening end 141.

A shielding member 19 is provided in the inlet tank 14 so that an inner surface of the circumferential wall 143 is unlikely to be exposed to the introduced exhaust gas. The shielding member 19 includes: a cylindrical inlet end 192 fitted in the inlet end 142 of the inlet tank 14 and welded thereto; an outlet end 191 with a square contour opened toward the rear side; and a circumferential wall 193 that connects the ends 191 and 192 to each other.

The contour of the outlet end 191 may be not a square but a circle or the like or may be appropriately determined in accordance with the sectional shape of the tubes 12, the shape of the end of the core 25, the shape of the opening end 141 of the inlet tank 14, or the like.

The opening area of the outlet end 191 is sufficiently large to entirely cover the entrances of all the tubes 12 arranged side by side, so that the introduced exhaust gas is equally fed into the tubes 12. The outlet end 191 is formed in the shape of a straight cylinder having a constant diameter along the flow direction of the exhaust gas (from front to rear) to allow a favorable feeding of the exhaust gas from the shielding member 19 into the tubes 12 without diffusion.

A slight clearance S is formed between the outlet end 191 and the header plate 13 (in FIG. 1, the clearance S is exaggerated to be easily visible). The clearance S is desirably narrowed not only for preventing the exhaust gas from flowing toward the circumferential wall 143 of the inlet tank 14 but also for smoothly directing the exhaust gas into the tubes 12. In view of the above, according to this exemplary embodiment, as long as the shielding member 19 does not contact with the header plate 13 even when the shielding member 19 is thermally expanded due to exposure to the exhaust gas having a high temperature, the clearance S is narrowed as much as possible.

The circumferential wall 193 is gradually widened from the inlet end 192 toward the outlet end 191. In other words, the opening area of the outlet end 191 is larger than the opening area of the inlet end 192. Incidentally, the shape of the circumferential wall 193 may be determined in accordance with the size of the inflow opening 16A. For instance, when the inflow opening 16A has a larger opening area and is widened with a dimension substantially equal to the vertical dimension of the tubes 12 in the figure, the circumferential wall 193 is formed in the shape of a straight cylinder identical to those of the inlet end 192 and the outlet end 191.

In the EGR cooler 10 according to this exemplary embodiment as described above, the exhaust gas having a high temperature introduced into the inlet tank 14 through the inflow opening 16A is guided by the shielding member 19 to be fed into the tubes 12 while hardly contacting with the circumferential wall 143. The exhaust gas passing through the tubes 12 is cooled by the cooling water flowing outside the tubes 12 in the casing 11 and is discharged into the outlet tank 15. The exhaust gas is returned to an air-intake side of the engine.

In the above manner, the exhaust gas is unlikely to contact with the circumferential wall 143 in the inlet tank 14, so that the thermal expansion of the circumferential wall 143 shown by a two-dot chain line in FIG. 3 can be significantly reduced to prevent deformation in the casing 11 and the header plate 13. In particular, prevention of deformation in the header plate 13 results in restraint of generation of stress at the bonding portion between the header plate 13 and each of the tubes 12 and thus prevention of a crack in an outer bonding portion.

It should be appreciated that the scope of the invention is not limited to the above exemplary embodiment but modifications and improvements that are compatible with an object of the invention are included within the scope of the invention.

For instance, although the inlet tank 14, the attachment flange 16 and the shielding member 19 are provided as separate bodies and are bonded together by welding or the like according to the above exemplary embodiment, these components may be molded into one piece component as shown in FIG. 6.

Although the shielding member 19 is provided in the inlet tank 14 according to the above exemplary embodiment, the shielding member 19 may be provided to the header plate 13.

The shielding member 19 may have a configuration in which the straight cylindrical outlet end 191 according to the above exemplary embodiment is omitted and the circumferential wall 143 is directly opened at the rear without departing the scope of the invention. However, the outlet end 191 is preferably provided because the outlet end 191 serves to efficiently guide a flow of the exhaust gas into the tubes 12.

Although the outlet end 191 has an opening area sufficiently large to cover the ends of all the tubes 12 according to the above exemplary embodiment, the outlet end 191 may have an opening area insufficiently large to cover the ends of all the tubes 12 without departing the scope of the invention. However, the opening area is preferably sufficiently large to cover the ends of all the tubes 12 because such an opening area serves to equally feed the exhaust gas into the tubes 12 as described above and thus cooling efficiency can be improved.

Further, since the shape of the circumferential wall 193 is optional, instead of the linearly widened shape according to the above exemplary embodiment, a round shape may be selected such that the circumferential wall 193 is curved as a whole. In other words, the shape of the circumferential wall 193 is appropriately selectable in implementation of the invention.

Although the above exemplary embodiment uses the flattened tubes 12 as the tubes according to the invention, tubes with a circular cross section may alternatively be used. In other words, tubes of any shape may be usable. When tubes with a circular cross section are used, it is preferable that the outlet end 191 of the shielding member 19 likewise has a circular shape.

Further, since the configuration of the header plate 13 is also optional, the cylindrical portion 131 as in the above exemplary embodiment may be omitted. In other words, the header plate 13 may be formed in a plate-like shape and bonded to the inner circumferential surface of the casing 11 at the outer circumference thereof Even in such a configuration, the thermal expansion of the circumferential wall 143 of the inlet tank 14 can cause deformation in the header plate 13 along with deformation in the casing 11 and thus a large stress is likely to be generated at the bonding section between the header plate 13 and each of the tubes 12. Accordingly, the invention is effectively applicable to prevent generation of stress.

INDUSTRIAL APPLICABILITY

The invention is suitably applicable to construction machines, transport vehicles and various industrial machines in which an engine having an EGR system is mounted.

EXPLANATION OF CODES

10...EGR cooler, 11...casing, 12... tube, 13...header plate, 14... inlet tank, 19...shielding member, 191...outlet end, S... clearance 

1. An EGR cooler comprising: a casing in which cooling water flows; a plurality of tubes in which exhaust gas flows, the plurality of tubes being housed in the casing; a header plate to which ends of the plurality of tubes are bonded, the header plate being bonded to an end of the casing; an inlet tank into which the exhaust gas is introduced, the inlet tank being bonded to the end of the casing; and a shielding member being provided in the inlet tank to shield a circumferential wall of the inlet tank from the introduced exhaust gas, the shielding member being fixed to the inlet tank with a clearance being formed between the shielding member and the header plate.
 2. (canceled)
 3. (canceled)
 4. The EGR cooler according to claim 1, wherein an opening of an exhaust gas outlet of the shielding member covers entrances of all the tubes.
 5. The EGR cooler according to claim 1, wherein the shielding member is gradually widened toward an exhaust gas outlet.
 6. The EGR cooler according to claim 4, wherein, the opening of the exhaust gas outlet is provided with a cylindrical outlet end having a diameter substantially constant along a flow direction of the exhaust gas. 